detect multiple file support and prefer tif

tiff files with an aux .tfw world file can get identified as either
depending upon the iteration sequence over the formats. if there
are more than 1 recognized file types and one is tiff, prefer tif.
Otherwise, blow up for any future collisions like this.
better logging for mismatched/empty file formats
better detection of aux files (shp.xml, etc.)

original algorithm could miss multi-extension auxillary files
causing problems with many unrecognized files showing up